Method and device for remote monitoring of led lamps

ABSTRACT

LED lamp circuitry that emulates an incandescent lamp&#39;s behavior upon remote verification of the LED lamp. The invention presents a fuse blow-out circuit and a cold filament detection circuit permitting the use of LED lamps in applications, such as railway signal light applications, where there is a need for remote monitoring of the lamps, while keeping the advantageous features of lower power consumption and longer life. The invention also provides a control circuit for enabling/disabling the power supply to LED lamps in relation to the level of the line voltage. The advantage of this embodiment is to avoid unwanted functioning of the LED lamp caused by interference from surrounding electrical cables.

RELATED APPLICATION

This is a continuation, of application Ser. No. 09/996,300, filed Nov.28. 2001, which is a continuation-in-part of U.S. application Ser. No.09/543,240 filed Apr. 5, 2000 now abandoned. Each of these priorapplications is hereby incorporated herein by reference, in itsentirety.

FIELD OF THE INVENTION

The present invention relates to the electric supply of light-emittingloads, in particular light-emitting diode (LED) lamps. Morespecifically, the present invention is concerned with electric circuitsand methods required for remote monitoring of LED lamps.

BACKGROUND OF THE INVENTION

Light-emitting diode (LED) lamps are becoming more and more popular inautomotive traffic lights, railway signal lights and other applications.Their lower power consumption is an attractive feature, but the mainreason for their popularity is their long life (100 000 hours) comparedto standard incandescent lamps (5 000 hours). Manifestly, these featuresallow important reduction in maintenance costs.

In certain applications, such as railway signal lights, these lamps maybe used, as those skilled in the art would know, for main linesignalling and/or grade crossing signalling. Grade crossing signals areusually situated in populated areas such as road intersections. Remotemonitoring of the LED lamps in grade crossing signals is therefore notnecessary. Main line signals, on the other hand, can be installed inremote areas, which are not easily accessible. Remote monitoring forchecking the integrity of the lamps signals is therefore commonpractice.

For lamps equipped with standard incandescent bulb, electrical integritycan be easily verified. If the filament of the incandescent bulb is innormal condition, current flows through the bulb according to Ohm's law(I=V/R). Otherwise, if the filament is open, no current flows throughthe bulb and it should be replaced.

For LED lamps, however, LED current is controlled by a power supply.Current characteristics are therefore not identical in a LED lamp and inan incandescent lamp. In a LED lamp, alternative current (ac) linevoltage is rectified and then converted to a suitable level by a dc-dc(direct current) converter, which also regulates LED current. In case ofLED failure, or failure of any other electrical component in the LEDlamp, it is possible for the power supply to continue drawing current ator near the nominal current value, even if the LED's are not emittingany light. Remote monitoring systems could therefore see the LED lamp asfunctioning correctly when in reality it is not. This situation is notacceptable since it can lead to very hazardous train operations andcause major accidents.

Another problem, related to LED lamps and their power supplies andcontrollers, is caused by electric components which retain residualvoltage differentials after power is removed from the LED lamp. Theresulting characteristic is that a LED lamp will effectively light upwhen the power applied to it reaches a first high level while it will beturned off only when the power reaches a second lower level. Theresulting problem is that if a certain power is induced by, for example,other nearby cables, the LED lamp could remain on while in fact itshould be off. This could also lead to dangerous situations.

These particularities of LED lamps limit their widespread use insituations where they need to be remotely monitored such as in railwaymain line signalling applications.

OBJECTS OF THE INVENTION

An object of the present invention is therefore to allow LED lamps tobecome compatible with remote detection systems designed for monitoringof incandescent lamps.

Another object of the invention is to provide LED lamp circuitry whichwill emulate an incandescent lamp's behaviour upon remote monitoring ofthe LED lamp.

Yet another object of the invention is to provide a control circuit forenabling/disabling the power supply to LED lamps in relation to thelevel of the line voltage.

SUMMARY OF THE INVENTION

More specifically, in accordance with the present invention, there isprovided a fuse blow-out circuit for establishing a short circuitbetween first and second voltage and current supply lines to blow out aprotection fuse through which a current supplied to a light-emittingload by the first and second lines flows, this fuse blow-out circuitcomprises:

a timer means responsive to the voltage across the first and secondlines for producing a time-representative signal after a certain periodof time;

means connected to the timer means for preventing production of thetime-representative signal in response to the current supplied to thelight-emitting load; and

means for establishing a current path between the first and second linesin response to the time-representative signal.

Accordingly, when no current is supplied to the light-emitting load, thecurrent path is established and provides the short circuit between thefirst and second lines that will blow out the protection fuse andemulate an open circuit of a defective incandescent lamp.

Also in accordance with the present invention, there is provided a fuseblow-out circuit for establishing a short circuit between first andsecond voltage and current supply lines to blow out a protection fusethrough which a current supplied to a light-emitting load by the firstand second lines flows. This fuse blow-out circuit comprises:

a resistor and a capacitor connected in series between the first andsecond lines, this resistor having a given resistance value, and thiscapacitor having a given capacitance value and a capacitor charge perioddependent on the given resistance value and the given capacitance value;

a trigger circuit connected in parallel with the capacitor, andcomprising a first controllable switch member closed in response to thecurrent supplied to the light-emitting load to discharge the capacitor;and

a second controllable switch member defining a current path between thefirst and second lines and closed in response to a given voltageamplitude across the capacitor.

Therefore, in the absence of current supplied to the light-emitting loadfor a duration equivalent to the capacitor charge period, the givenvoltage amplitude across the capacitor is reached to thereby close thesecond switch member, establish the current path and provide the shortcircuit between the first and second lines that will blow out theprotection fuse and emulate an open circuit of a defective incandescentlamp.

Further in accordance with the present invention, there is provided apower supply unit responsive to alternating voltage and current from anac source for supplying a dc voltage and current to a light-emittingload, comprising:

a rectifier unit rectifying the alternating voltage and current from theac source and supplying the rectified voltage and current to first andsecond voltage and current supply lines;

a protection fuse through which the alternating current from the acsource is supplied to the rectifier unit;

a converter of the rectified voltage and current into the dc voltage andcurrent supplied to the light-emitting load;

a fuse blow-out circuit as described above, for establishing a shortcircuit between the first and second voltage and current supply lines toblow out the protection fuse; and

a controller of the converter in response to the rectified voltage onthe first and second lines.

The present invention also relates to a cold filament detection circuitconnected between first and second lines through which a voltage andcurrent supply source supplies voltage and current to a light-emittingload, the voltage and current supply source having a set up time duringwhich no current is supplied to the light-emitting load. This coldfilament detection circuit comprises:

a resistor;

means for connecting the resistor between the first and second lines inresponse to the voltage on the first and second lines to therebyestablish through this resistor a current path between the first andsecond lines; and

means for disconnecting the resistor from between the first and secondlines in response to the current supplied to the light-emitting load.

Accordingly, during the set up time no current is supplied to thelight-emitting load and the current path is established through theresistor to emulate the impedance of an incandescent lamp, and whencurrent is supplied to the light-emitting load, the resistor isdisconnected from between the first and second lines.

The present invention further relates to a cold filament detectioncircuit connected between first and second lines through which a voltageand current supply source supplies voltage and current to alight-emitting load, the voltage and current supply source having a setup time during which no current is supplied to the light-emitting load.The cold filament detection circuit comprises:

a resistor;

a controllable switch member: connected in series with the resistorbetween the first and second lines; responsive to the voltage on thefirst and second lines; and having a current-conductive junctionestablished in response to the voltage on the first and second lines tothereby establish through the resistor a current path between the firstand second lines; and

a switch control unit responsive to the current supplied to thelight-emitting load, connected to the first controllable switch member,and having a switch-disabling circuit which prevents thecurrent-conductive junction to establish as long as current is suppliedto the light-emitting load.

In operation, during the set up time no current is supplied to thelight-emitting load and the current path is established through theresistor to emulate the impedance of an incandescent lamp, and whencurrent is supplied to the light-emitting load, the switch-disablingcircuit prevents the current-conductive junction to establish wherebythe resistor is disconnected from between the first and second lines.

The present invention still further relates to a voltage and currentsupply source responsive to alternating voltage and current from an acsource for supplying dc voltage and current to a light-emitting load,comprising:

a rectifier unit rectifying the alternating voltage and current from theac source and supplying the rectified voltage and current to first andsecond voltage and current supply lines;

a converter of the rectified voltage and current into the dc voltage andcurrent supplied to the light-emitting load;

a cold filament detection circuit as defined above, connected betweenthe first and second lines through which the voltage and current supplysource supplies voltage and current to the light-emitting load; and

a controller of the converter in response to the rectified voltage onthe first and second lines.

The present invention is also concerned with a voltage control circuitfor controlling the amplitude of a voltage signal on a control terminalof a power controller unit itself controlling a voltage and currentsupply source which supplies a current to a light-emitting load throughfirst and second voltage and current supply lines. This voltage controlcircuit comprises:

means for producing a first trigger voltage in response to the voltageacross the first and second lines, this first trigger voltage having anamplitude representative of the amplitude of the voltage across thefirst and second lines;

first switch means, connected in series with a high impedance elementbetween the control terminal and one of the first and second lines, forestablishing a high impedance current path between the control terminaland said one line when the first trigger voltage reaches a givenamplitude, wherein the first switch means comprises means for producinga second trigger voltage having a first amplitude when the highimpedance current path is not established and a second amplitude whenthe high impedance current path is established; and

second switch means, connected in series with a low impedance elementbetween the control terminal and said one line, for establishing a lowimpedance current path between the control terminal and said one linewhen the second trigger voltage has the first amplitude.

Accordingly, when the first trigger voltage has an amplitude lower thanthe given amplitude, the high impedance current path is not established,a second trigger voltage of first amplitude is produced, and the lowimpedance current path is established to result in a voltage signalamplitude on the control terminal which disables the power controllerunit and, when the amplitude of the first trigger voltage reaches thegiven amplitude, the high impedance current path is established, asecond trigger voltage of second amplitude is produced, and the lowimpedance current path is not established to result in a voltage signalamplitude on the control terminal which enables said power controllerunit.

The present invention is further concerned with a voltage controlcircuit for controlling the amplitude of a voltage signal on a controlterminal of a power controller unit itself controlling a voltage andcurrent supply source which supplies a current to a light-emitting loadthrough first and second voltage and current supply lines. The voltagecontrol circuit comprises:

a voltage divider circuit connected between the first and second linesand comprising resistors which divide the voltage on the first andsecond lines to produce a first trigger voltage signal;

a first controllable switch member connected in series with a highimpedance element between the control terminal and one of the first andsecond lines to define a high impedance current path between thiscontrol terminal and said one line, this first controllable switchmember being responsive to the first trigger voltage signal and having afirst current-conductive junction established when the first triggervoltage reaches a given amplitude, wherein the high impedance currentpath produces a second trigger voltage having a first amplitude when thefirst current-conductive junction is not established and a secondamplitude when the first current-conductive junction is established; and

a second controllable switch member connected in series with a lowimpedance element between the control terminal and said one line todefine a low impedance current path between this control terminal andsaid one line, this second controllable switch member being responsiveto the second trigger voltage and having a second current-conductivejunction established when the second trigger voltage has the firstamplitude and non established when the second trigger voltage signal hasthe second amplitude.

Therefore, when the first trigger voltage has an amplitude lower thanthe given amplitude, the first current-conductive junction is notestablished to produce in the high impedance current path a secondtrigger voltage of first amplitude which establishes both the secondcurrent-conductive junction and the low impedance current path to resultin a voltage signal amplitude on the control terminal which disables thepower controller unit and, when the amplitude of the first triggervoltage reaches the given amplitude, both the first current-conductivejunction and the high impedance current path are established to producein the high impedance current path a second trigger voltage of secondamplitude whereby both the second current-conductive junction and thelow impedance current path are not established to result in a voltagesignal amplitude on the control terminal which enables the powercontroller unit.

The present invention is still further concerned with a voltage andcurrent supply source responsive to alternating voltage and current froman ac source for supplying dc voltage and current to a light-emittingload, comprising:

a rectifier unit rectifying the alternating voltage and current from theac source and supplying the rectified voltage and current to first andsecond voltage and current supply lines;

a converter of the rectified voltage and current into the dc voltage andcurrent supplied to the light-emitting load;

a power controller unit having a control terminal and controlling theconverter in response to the rectified voltage on the first and secondlines; and

a voltage control circuit as described above, for controlling theamplitude of a voltage signal on the control terminal of the powercontroller unit.

The embodiments described herein present the advantage that they permitthe use of LED lamps in applications, such as railway signal lightapplications, where there is a need for remote monitoring of the lamps,while keeping the advantageous features of lower power consumption andlonger life.

Other objects, advantages and features of the present invention willbecome more apparent upon reading of the following non-restrictivedescription of preferred embodiments thereof, given by way of exampleonly with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the appended drawings:

FIG. 1 is a schematic block diagram showing a LED lamp assemblyincluding a fuse blow-out circuit, a cold filament detection circuit,and a turn-off voltage circuit;

FIG. 2A is a schematic electrical circuit diagram of a first embodimentof a fuse blow-out circuit according to the invention;

FIG. 2B is a schematic electrical circuit diagram of a second embodimentof the fuse blow-out circuit according to the invention;

FIG. 2C is a schematic electrical circuit diagram of a third embodimentof the fuse blow-out circuit according to the invention;

FIG. 3 is a schematic electrical circuit diagram of a cold filamentdetection circuit in accordance with the present invention; and

FIG. 4 is a schematic electrical circuit diagram of a turn-off voltagecircuit according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, an ac (alternating current) line voltage issupplied to a LED lamp B by a voltage and current supply source 10through a line 11. The AC line voltage is EMI (ElectromagneticInterference) filtered and surge suppressed by means of functional block12 including an EMI filter, a surge suppressor and an input fuse. Then,the line voltage is rectified through a rectifier 14 and subsequentlyconverted to a DC voltage through a DC-DC converter 20. The DC voltagefrom the converter 20 is supplied on line 21 to light up aseries/parallel LED (light-emitting diodes) array 22. LEDs are also moregenerally referred to in the present, specification as light-emittingloads.

The current flowing through the series/parallel LED array 22 is sensedby a current sensor 100. This current sensor 100 produces a LED currentsense signal 23 supplied to a power factor controller 28. The functionof the power factor controller 28 is to control the DC-DC converter 20through a line 27, which in turn controls the DC current and voltage online 21.

In the illustrated example, the series/parallel LED array 22 is formedof a plurality of subsets 26 of five (5) serially interconnectedlight-emitting diodes 24. Each subset 26 of serially interconnectedlight-emitting diodes 24 are connected in parallel to form theseries/parallel LED array 22. A particularity is that the anodes of thefirst light-emitting diodes of the subsets 26 are interconnected, thecathodes the first light-emitting diodes of the subsets 26 and theanodes of the second light-emitting diodes of the subsets 26 areinterconnected, the cathodes of the second light-emitting diodes of thesubsets 26 and the anodes of the third light-emitting diodes of thesubsets 26 are interconnected, the cathodes of the third light-emittingdiodes of the subsets 26 and the anodes of fourth light-emitting diodesof the subsets 26 are interconnected, the cathodes of the fourthlight-emitting diodes of the subsets 26 and the anodes of the fifthlight-emitting diodes of the subsets 26 are interconnected, and thecathodes of the fifth light-emitting diodes of the subsets 26 areinterconnected. Of course, other types of arrangements comprisingvarious numbers of LEDs are possible within the scope of the presentinvention.

Various embodiments of EMI filter (block 12), surge suppressor (block12), input fuse (block 12), rectifier 14 and DC-DC converter 20 can beused. These embodiments are well known to those of ordinary skill in theart and, accordingly, will not be further described in the presentspecification. Also, in a preferred embodiment of the invention, aMotorola® MC33262P integrated circuit (IC) chip is used as power factorcontroller 28. However, it is within the scope of the present inventionto use other IC chips commercially available on the market, or that willbecome available on the market in the future.

FIG. 1 shows a fuse blow-out circuit 16, a cold filament detectioncircuit 18 and a turn-off voltage circuit 30. These circuits will bedescribed in greater detail hereinafter.

Fuse Blow-Out Circuit

Referring to FIG. 2A, a first embodiment of the fuse blow-out circuit isshown and generally designated by the reference 16. The fuse blow-outcircuit 16 receives the rectified voltage from output terminal 15 of therectifier 14 on an input 48. The fuse blow-out circuit 16 also comprisesa second input 49 to receive the LED current sense signal 23 from thecurrent sensor 100. As long as no LED current sense signal 23 appears onthe input 49, a FET (Field-Effect Transistor) transistor 42 is turnedoff. While transistor 42 is turned off, capacitor 34 is being chargedthrough resistor 31 and diode 32 from the voltage supplied on the input48. Concurrently, capacitor 41 is being charged through resistor 31,diode 32 and resistor 37. When the voltage across capacitor 41 reachesthe breakdown voltage of Zener diode 40 having its anode groundedthrough resistor 47 (while transistor 42 is still turned off), siliconbilateral switch (or triac) 38 turns on to supply a current to a triggerelectrode 103 of a thyristor 39 to thereby trigger this thyristor 39.Triggering of the thyristor 39 into conduction creates a short-circuitbetween output terminal 15 of rectifier 14 (see FIGS. 1 and 2A) and aground output terminal 101 of the same rectifier 14.

This short-circuit will effectively blow out the input fuse offunctional block 12, thereby opening the circuit. Detection of that opencircuit will indicate that the lamp is defective thereby emulating theopen circuit of a defective incandescent lamp.

It is to be noted that the sequence of events described above will onlytake place after a given period of time (fuse blow-out time) has lapsedduring which no current is sensed by current sensor 100. This givenperiod of time is constant and is dependent on the values of resistor31, resistor 33, resistor 35 and capacitor 34.

If, on the other hand, a LED current sense signal 23 is supplied to theinput 49 prior to the end of the above mentioned given period of time,this LED current sense signal 23 is applied to the gate electrode 102 ofFET transistor 42 through resistor 43 to turn this transistor 42 on.Capacitor 41 then discharges to the ground 101 through resistor 36 andthe source/drain junction of transistor 42. Accordingly, capacitor 41will never become fully charged, the breakdown voltage of Zener diode 40will never be reached, and no short circuit will be created between theterminals 15 and 101 of rectifier 14. Then, the input fuse of functionalblock 12 will remain intact.

Referring to FIG. 2B, a second embodiment of the fuse blow-out circuitis shown and still designated by the reference 16. Again, the fuseblow-out circuit 16 comprises the input 48 to receive the rectifiedvoltage from terminal 15 of the rectifier 14. The fuse blow-out circuit16 also comprises the second input 49 receiving the LED current sensesignal 23 from the current sensor 100 (FIG. 1). As long as no LEDcurrent sense signal 23 appears on the input 491 FET transistor 42 isturned off when transistor 42 is turned off, capacitor 34 is beingcharged through resistor 31 and diode 32 from the voltage supplied onthe input 48, when the voltage across the capacitor 34 reaches thebreakdown voltage of the Zener diode 44, (while transistor 42 is stillturned off) Zener diode 44 starts conducting current. A current is thensupplied to the base of a PNP transistor 45 through resistor 31, diode32 and Zener diode 44 to turn this transistor 45 on. When turned on, thecollector/emitter junction of the transistor 45 becomes conductive tosupply a current to the gate electrode of a FET transistor 46. Thisturns the FET transistor 46 on to establish a short circuit betweenoutput terminals 15 and 101 of the rectifier 14 through the source/drainjunction of the FET transistor 46. As illustrated, the emitter of thetransistor 45 and the gate electrode of the transistor 46 are bothconnected to the ground through a resistor 47.

Alternatively, as shown in FIG. 2C, the Zener diode 44, transistor 45and resistor 47 have been removed, and resistor 36 connected to the baseof transistor 46.

This short circuit will effectively blow out the input fuse of block 12,thereby opening the circuit. Detection of that open circuit willindicate that the LED lamp 8 is defective thereby emulating the opencircuit of a defective incandescent lamp.

It should be noted that the sequence of events described above will onlytake place after a given period of time (fuse blow-out time) has lapsedduring which no LED current sense signal 23 appears on the input 49.This given period of time is constant and depends on the values ofresistor 31, resistor 33, resistor 35 and capacitor 34.

If, on the other hand, the LED current sense signal 23 appears on theinput 49 prior to lapsing of the above mentioned given period of time,this signal 23 is supplied to the gate electrode 102 of FET transistor42 to thereby turn transistor 42 on. This connects the positive terminalof capacitor 34 to ground 101 through resistor 36 to thereby dischargecapacitor 34. In this case, the breakdown voltage of Zener diode 44 willnever be reached, transistor 45 will remain turned off, and no shortcircuit will be created between output terminals 15 and 101 of rectifier14. The input fuse of block 12 will, in this case, remain intact.

It should be noted that the “fuse blow-out time” must be longer than the“LED current set up time”. For example, in an embodiment, the LEDcurrent set up time is approximately 100 msec. Just a word to specifythat the “LED current set up time” is the period of time betweenswitching the LED lamp on and appearance of the LED current sense signal23 at input 49.

Cold Filament Detection Circuit

The cold filament detection circuit 18 of FIG. 3 is used to simulate anincandescent lamp as seen by a lamp proving system. Lamp proving isusually performed by sending a voltage pulse on the voltage supply line11, and verifying that current rises to a certain level, within acertain period of time. This represents the behaviour of an incandescentlamp, which is equivalent to a simple resistor.

A LED lamp uses a power supply which has a current set up time.Therefore, when sending a pulse on line 11, the current will not riseimmediately, but only after the power factor controller 28 is turned on(for example after about 100 msec in an embodiment). The cold filamentdetection circuit 18 of FIG. 3 solves this problem.

As soon as power is supplied on line 11, the voltage drop acrossresistor 51, connected between the output terminal 15 (input 56 of thecold filament detection circuit 18) and a gate electrode 104 of a FETtransistor, will turn on this transistor 53. This will connect resistor52 between the output terminals 15 and 101 of the rectifier 14.

When power is applied on line 11 for a period of time which is longerthan the LED current set up time, the LED current sense signal 23 willbe supplied on an input 57 of the cold filament detection circuit 18.This signal 23 is applied to the base 105 of a PNP transistor 54 to turnon this transistor 54 thereby turning transistor 53 off by forcing itsgate electrode 104 to the ground 101. The cold filament detectioncircuit 18 is thereby disabled to enable the LED lamp 8 to operatenormally. Biasing resistor 50 and Zener diode 55 are connected in seriesbetween the input 56 and the base electrode 105. Biasing resistor 50 isalso used for overvoltage protection.

The cold filament detection circuit 18 also serves as a back up for thefuse blow-out circuit 16. If fuse blow-out circuit 16 was to fail (thatis, it does not cause a short circuit to blow out the input fuse ofblock 12 when in fact it should), transistor 53 would remain turned onsince no LED current sense signal 23 would appear on input 57. Thecurrent draw through resistor 52 is sufficiently high to blow out theinput fuse of block 12 after a certain period of time. For example, inan embodiment of the invention, this time period is of a few minutes.

Turn Off Voltage Circuit

The turn-off voltage circuit 30 of FIG. 4 simply inhibits the powerfactor controller 28 (see FIG. 1) when the input voltage on line 11 ofthe circuit 30 is below a first predetermined trigger voltage.

The turn-off voltage circuit 30 comprises an input 70 supplied with thevoltage on the output terminal 15 of the rectifier 14. The firstpredetermined trigger voltage 72 is determined by a voltage dividercomprising resistors 60 and 69 serially connected between the input 70of the turn-off voltage circuit 30 and the ground 101. The firstpredetermined trigger voltage is established after a capacitor 68 hasbeen charged through the resistor 60 and the diode 61, i.e. after agiven period of time following application of the voltage on the input70. This period of time is determined by the values of the resistors 60,69 and 107 and of the capacitor 68.

The first predetermined trigger voltage 72 is applied to a gateelectrode 106 of a FET transistor 65 through the diode 61. when thefirst trigger voltage 72 reaches the breakdown voltage of the gateelectrode 106 of the FET transistor 65, transistor 65 is turned on.

The turn-off voltage circuit 30 comprises a terminal 71 connected to acontrol terminal 29 of the power factor controller 28. Before thetransistor 65 is turned on, the power factor controller 28 produces avoltage drop across high impedance resistor 62, to thereby produce asecond trigger voltage 73, which in turn turns on a FET transistor 63.This in turn creates a low impedance path comprising resistor 67 betweenterminal 29 of the power factor controller 2 and the ground 101. As longas transistor 63 is turned on, the voltage on terminal 29 of powerfactor controller 28 will be lower than the voltage level required toturn on the power factor controller 28.

When transistor 65 is turned on, this will modify the second triggervoltage 73 thereby turning off transistor 63. The voltage on terminal 29will then reach the level required to turn on the power factorcontroller 28, due to the high impedance value of the resistor 62.

Note that the LED lamp 8 will not be turned on until the first triggervoltage 72 is reached and once the lamp 8 is lit, it will stay on untilthe voltage on input 70 produces a first trigger voltage 72 which isbelow the transistor 65 trigger voltage (breakdown voltage of the gateelectrode 106).

Although the present disclosure describes particular types oftransistors in the different circuits of FIGS. 2A, 2B, 3 and 3, itshould be kept in mind that these different types of transistors can besubstituted or replaced by other available types of transistors.

Although the present invention has been described hereinabove by way ofpreferred embodiments thereof, it can be modified, without departingfrom the spirit and nature of the subject invention as defined in theappended claims.

What is claimed is:
 1. A voltage control circuit for controlling theamplitude of a voltage signal on a control terminal of a powercontroller unit itself controlling a voltage and current supply sourcewhich supplies a current to a light-emitting load through first andsecond voltage and current supply lines, said voltage control circuitcomprising: a) a voltage divider circuit connected between said firstand second lines and comprising resistors which divide the voltage onthe first and second lines to produce a first trigger voltage signal; b)a first controllable switch member connected in series with a highimpedance element between said control terminal and one of said firstand second lines to define a high impedance current path between saidcontrol terminal and said one line, said first controllable switchmember being responsive to the first trigger voltage signal and having afirst current-conductive junction established when the first triggervoltage reaches a give amplitude, wherein the high impedance currentpath produces a second trigger voltage having a first amplitude when thefirst current-conductive junction is not established and a secondamplitude when the first current-conductive junction is established; andc) a second controllable switch member connected in series with a lowimpedance element between said control terminal and said one line todefine a low impedance current path between said control terminal andsaid one line, and second controllable switch member being responsive tothe second trigger voltage and having a second current-conductivejunction established when the second trigger voltage has the firstamplitude and non established when the second trigger voltage signal hasthe second amplitude; whereby, when said first trigger voltage has anamplitude lower than said given amplitude, the first current-conductivejunction is not established to produce in the high impedance currentpath a second trigger voltage of first amplitude which establishes boththe second current-conductive junction and the low impedance currentpath to result in a voltage signal amplitude on said control terminalwhich disables said power controller unit and, when the amplitude of thefirst trigger voltage reaches said given amplitude, both the firstcurrent-conductive junction and the high impedance current path are asecond trigger voltage of second amplitude whereby both the secondcurrent-conductive junction and the low impedance current path are notestablished to result in a voltage signal amplitude on said controlterminal which enables said power controller unit.
 2. A voltage controlcircuit as in claim 1, wherein said light-emitting load comprises alight-emitting diode.
 3. A voltage control circuit as in claim 2,wherein said high impedance current path comprises a first resistor andsaid low impedance current path comprises a second resistor.
 4. Avoltage control circuit as in claim 3, wherein said first controllableswitch member comprises a first transistor having a control electroderesponsive to said first trigger voltage.
 5. A voltage control circuitas in claim 4, wherein said second controllable switch/member comprisesa second transistor having a control electrode responsive to said secondtrigger voltage signal.
 6. A voltage and current supply source as inclaim 3, wherein said first controllable switch member comprises a firsttransistor having a control electrode responsive to said first triggervoltage.
 7. A voltage and current supply source as in claim 4, whereinsaid second controllable switch member comprises a second transistorhaving a control electrode responsive to said second trigger voltagesignal.
 8. A voltage and current supply source responsive to alternatingvoltage and current from an ac source for supplying dc voltage andcurrent to a light-emitting load, comprising: a) a rectifier unitrectifying the alternating voltage and current from the ac source andsupplying the rectified voltage and current to first and second voltageand current supply lines; b) a converter of the rectified voltage andcurrent into the dc voltage and current supplied to the light-emittingload; c) a power controller unit having a control terminal andcontrolling the converter in response to the rectified voltage on thefirst and second lines; and d) a voltage control circuit as in claim 1,for controlling the amplitude of a voltage signal on the controlterminal of the power controller unit.
 9. A voltage and current supplysource as in claim 8, wherein said high impedance current path comprisesa first resistor and said low impedance current path comprises a secondresistor.
 10. A voltage control circuit for controlling the amplitude ofa voltage signal on a control terminal of a power controller unit itselfcontrolling a voltage and current supply source which supplies a currentto a light-emitting load through first and second voltage and currentsupply lines, said voltage control circuit comprising: a) means forproducing a first trigger voltage in response to the voltage across thefirst and second lines, said first trigger voltage having an amplituderepresentative of the amplitude of the voltage across the first andsecond lines; b) first switch means, connected in series with a highimpedance element between said control terminal and one of said firstand second lines, for establishing a high impedance current path betweensaid control terminal and one of said lines when the first triggervoltage reaches a given amplitude, wherein said first switch meanscomprises means for producing a second trigger voltage having a firstamplitude when the high impedance current path is not established and asecond amplitude when the high impedance current path is established;and c) second switch means, connected in series with a low impedanceelement between said control terminal and one of said lines, forestablishing a low impedance current path between said control terminaland one of said lines when the second trigger voltage has the firstamplitude; whereby, when said first trigger voltage has an amplitudelower than said given amplitude, the high impedance current path is notestablished, a second trigger voltage of first amplitude is produced,and the low impedance current path is established to result in a voltagesignal amplitude on said control terminal which disables said powercontroller unit and, when the amplitude of the first trigger voltagereaches said given amplitude, the high impedance current path isestablished, a second trigger voltage of second amplitude is produced,and the low impedance current path is not established to result in avoltage signal amplitude on said control terminal which enables saidpower controller unit.